A statement by the Foreign Relations Department released on Sunday said that executing Edgar Tamayo would be another US violation of an international treaty. Tamayo is set for lethal injection on Wednesday, for the 1994 fatal shooting of a police officer who had arrested him for a robbery.

Mexico has been asking the US to halt Tamayo's execution because the inmate was not told he could get legal help from the Mexican government, as agreed under the 1963 Vienna Convention on Consular Relations.

As part of what is often dubbed the “Avena decision”, the ICJ ordered the US to review and reconsider the convictions and sentences to decide if they had been influenced by the violations of consular rights.

Tamayo's lawyers say assistance from the Mexican consulate could have helped Tamayo obtain mitigating evidence to persuade jurors to choose a punishment other than death.

In its statement on Sunday, the Mexican government said the Tamayo case was “a clear violation by the United States of its international obligations under the Vienna Convention, whose observance is fundamental to guaranteeing the right of any person to due process, including United States nationals, travelling or living abroad”.

The statement added: “Mexico appreciates the efforts of the government of the United States to ensure that the state of Texas respects the Avena decision as well as the repeated recognition of its international obligation … and the efforts … to seek passage of a bill that would ensure the compliance of all the states with this international obligation; legislation which unfortunately remains unrealised.”